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Member postings for Hugh Gilhespie

Here is a list of all the postings Hugh Gilhespie has made in our forums. Click on a thread name to jump to the thread.

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Thread: de-scaling steel boilers
27/11/2011 17:24:51
The idea that deionised and distilled water have different properties is a myth.
Different processes certainly. End result is exactly the same though - pure water with the same properties regardless of the way it was obtained
.
Distillation is very energy intensive and very difficult to get very pure water due mainly to entrained droplets in the steam. Ion exchange is cheaper and with good quality resins gives very pure water.
 
I don't know owt about small boilers but on an industrial scale all high pressure boilers run on deionised water. Usually a minimum of three treatment stages for raw water, anion, cation and finally mixed bed polishing. After all that the water is treated with steam to remove dissolved gases, particularly oxygen, before going to the feed water pumps. The recirculating condensate is sometimes put through a mixed bed unit to clean it up before being reused. Water treatment quality is probably the single most important factor in the time the boiler will operate between outages.
 
Regards, Hugh
 
27/11/2011 14:30:47
Hi Jason,
 
'Deionised and distilled water are two different things'
 
Are you really, really sure ? Because if you are I would guess you are up for a Nobel prize
 
Regards, Hugh
Thread: Slitting saw thickness
27/11/2011 09:45:12
Hi Skarven
 
This link has some useful information on slitting saws on page 13.
 
Regards, Hugh
Thread: de-scaling steel boilers
27/11/2011 09:20:56
Hi Heronsgate,
 
The choice of 'best' descaling treatment for a steel boiler depends on what the scale is. Unless the boiler has been run on deionised (distilled) water it is likely that a lot of the scale will be hard water salts, calcium carbonates and sulphates typically. This is actually more difficult to remove than iron oxide (magnetite) scale and I wouldn't use phosphoric acid based products because it will form a layer of calcium phospate which is very insoluble and stop any futher action of the acid. The same will apply to using sulphuric acid which forms calcium sulphate.
 
If it is a hard water scale - easy to tell as the scale will be a greyish colour I would recommend dilute, say 5% hydrochloric acid, fairly warm 40 - 60 C and with agitation. DON'T seal the boiler as there will probable be some CO2 released and DON'T leave it in any longer than needed. Hydrochloric acid will attack the steel. It is possible to inhibit the attack on the underlying metal with special chemicals but these are not easy to come by. So, fill, agitate for say 10 minutes, pour out and have a look. If the scale is still there put the acid back in and repeat until the scale has gone. Usual warnings about using acids, good PPE including very good goggles, wash off any splashes immediately.
 
If the scale is a nice dark brown or black then it is probably nearly all iron oxide and hopefully mostly magnetite. This will dissolve easily in most acids so use the safest acid. Personally I would use citric acid at about 6% and 50 C. Will take a couple of hours to dissolve the scale and you may get some copper plating - not a serious problem.
Again DON'T leave it in any longer than you need - you are losing precious metal thickness!
 
Hope this helps,
 
Regards, Hugh
Thread: metric taps
23/11/2011 17:40:11
Hi Jason
 
Still no answer to what the total engagement percentage is based on.
 
Oops - I thought I did
 
Regards, Hugh
23/11/2011 11:11:54
For metric and American threads with a 60 degree thread form the calculation of the percentage engagement is straightforward as the thread form is an isosceles triangle.
 
The full 'sharp' height of the thread is Pitch x SQRT(1 - (0.5^2)). Then multiply by 2 for thread height on both sides of the diameter. This gives
 
'Sharp' Thread depth (without corner rounding) = Pitch * SQRT(1-(0.5^2))*2 = Pitch * 1.732051.
 
But both the crests and roots of the threads are flattened. The crest by 1/8th of the height and the root by 1/4 of the height. So, the actual thread height is 5/8th of the sharp tooth height.
 
So, finally the working thread depth is given by Pitch * 1.082532.
 
To calculate the tapping hole size for a given percentage engagement, use the formula
 
Tapping size = Major Diameter - (1.08253 * Pitch * Percent Engaged/100)
This is the formula given in Machinery's Handbook.
 
So, for an Iso M8 coarse, pitch is 1.25 mm, major diameter = 8 mm and for say 60% engagement the tapping size is 7.188 mm. In reality, use a 7.2 mm tapping drill and this will give about 59% thread engagement.
 
If you don't want to bother with calculations, Harold Hall's website has a very good section on selecting tapping sizes showing a range of thread engagements.
 
Hope this helps.
 
Regards, Hugh
 
Thread: Bridgeport leadscrew adjustment.
20/11/2011 10:05:37
Hi Roy

This link has a very good discussion on adjusting the backlash on a Bridgeport.
 
Regards, Hugh
Thread: help with pump design
17/11/2011 22:59:22
Probably just me, but if that's a ball valve on the right, in the air intake, surely it will never open?
 
Hugh
Thread: New Blocks on the Block
17/11/2011 14:41:29
I think it's appalling. Blatant advertising. No one should buy these blocks............
 
At least until after I've got the one's I've ordered
Thread: Lathe alignment. What is good enough?
07/11/2011 17:16:00
Hi Terry,
 
My projects ARE amazing. At least in the sense that I am amazed that I have actually made something that actually works! Doesn't matter if it doesn't work very well or all the mistakes along the way - just being able to create something myself gives me a real thrill. It's not false modesty when I say I am not very good at this, just the simple truth but you have to start somewhere.
 
Not only do I like the idea of having the basic kit in good working condition, for someone with as little experience as I have, it is an absolute necessity. I just don't have the craftsmanship or experience to fall back on so I rely totally on the equipment I use. If I am feeling optimistic, perhaps I will get better and develop more skills but it's not guaranteed and in fact not even needed. I get a huge amount of satisfaction from what I can do now.
 
Regards, Hugh
 
07/11/2011 17:05:51
Hi,
 
I do have some issues with the headstock taper. With the test bar fitted, I get a TIR of about 0.5 thou close to the head and about 1-2 thou at the end of the bar. The actual taper in the spindle is an MT5 I think and I have an MT5 / MT3 adapter that came with the lathe - a Colchester Student 1800 of 1975-6 vintage. The adapter has taken a few knocks in the last 35 years and is a bit battered. This is why I am looking at Rolley's Dad's method for initial alignment . I do agree with Martin that the final and most useful test is by measuring diameters after careful cuts.
 
I also know that the bed is not level and I am hoping that getting it level and twist free will do everything I want. I will adjust the headstock if I have to but I am hoping fervently that I don't have to!
 
I think the spindle bearings are OK - or at least, when I clock on a freshly turned piece of bar there is no measurable run out - none detectable at all and I hope that means that the bearings are good.
06/11/2011 22:07:44
Hi Steve and Skarven,
 
Thanks for the link. I do have that one - and some others that disagree with it! But, I guess it works so I will stick with it.
 
What I am planning on doing is using my test bar as the rod in the Rolley's Dad's method. It's a bit shorter than recommended, about 6 inches after the taper but at least I know it is accurately concentric.
 
Yes, they are a bit pricey, about £80 for the MT3 as I recall, but they are beautifully made and I decided to invest in some kit that will let me set up the lathe as accurately as I can. That way, I will know for certain that all the cock-ups are down to me alone! I have made a couple of dedicated DTI holders that fit into the normal tool holders on the QCTP, one for horizontal and one for vertical alignment.
 
The idea is that by having the kit easily to hand, I can check and adjust the lathe on a fairly regular basis. I also intend to make a face plate attachment for mounting a DTI to allow accurate re-centering of the tail stock - knowing that I can re-centre it easily I will be more inclined to use a set over tail stock for taper turning, etc.
 
I have also paid a bit of attention to the adjustable feet for the lathe. These need to lift the lathe about 4 inches so I can use a pallet truck for moving it as required. However, I didn't fancy long studs, too much vibration, so I am using lengths of 2 inch bar for the main supports with fairly short studs that will allow plus or minus 0.5 inch height adjustment. The studs are M12 by 1 so one full turn of the nut will give a 40 thou height change. The nuts will also be made from 2 inch bar and fitted with tommy bar holes. Conventional hex nuts will be used to lock the main nuts after adjustment. I will use soft copper washers between the nuts and the lathe to bed down onto the casting.
 
If I can get anywhere near the accuracy that Skarven has achieved I will be a very happy bunny.
 
Regards, Hugh
06/11/2011 18:23:14
Hi Skarven,
 
Can you give a link to the 'Rollie's Dad's method that you used for checking alignment? I have looked at a couple of sites that give this method and they seem to contradict each other so it would be interesting to see which one you used.
 
I am just about to try and set up my lathe using this technique - or I will be when I have finished making new six new adjusting feet - why Colchester think 6 feet are required is a mystery but they do, so 6 off feet it is.
 
I have an Arrand test bar all ready to go and a ludicrously accurate and cheap dial indicator from CTC Tools, the dial reads in microns and it has a 1 mm range. It does seem to be accurate as well, or at least it agrees with the DRO on the lathe. Quite frightening to use as you think the run out is huge until you realise that it's only a quarter of a thou that's making the neeedle move 5 or 6 divisions.
 
Just need to get the beast level.....
 
Regards, Hugh
Thread: Issue using Google Chrome
05/11/2011 09:25:07
Well done Ed!!!
 
I was getting exactly the same results as you described but I assumed it was me doing something daft! I found the only way to add a posting was to write it using Notepad then Paste Plain Text into the window, a right royal pain!
 
So, if this post appears, typed directly into the Post a Reply text box it will be a great advance.
 
Regards, Hugh
Thread: Small Steel Boilers
02/11/2011 08:52:21


Hi,

Once again a content warning! My brain is slowly but surely leaking away all the information it used to have, and as all this is based on stuff I did 20 years ago it cannot be considered reliable!

Next a couple of corrections, senior moments in my earlier post. I got my chromium and molybdenum the wrong way round, the correct figures for ASTM A335 Grade P22 is 2.25% chromium and 1 % molybdenum.

Finally, for some fairly gentle information on magnetite films in boilers, this is a good link.


http://www.angelfire.com/mt/chemicalcleaning/magnetite.html

Regards, Hugh

Thread: screwcutting from a shoulder
01/11/2011 08:19:27

An universal attachment (requiring no customization) being able to stop the tool near the shoulder and even to retract it would be a good thing, does it exist?.....

Think it's called CNC

Thread: Small Steel Boilers
31/10/2011 23:29:27


Hi Alf,
My information is a bit out of date but and my memory is also suspect but as far as I recall, the ASME codes for steel steam piping require about a 10% thickness increase to allow for corrosion in service. There is also another, smaller allowance for toleraance on wall thickness.
As far as boiler corrosion is concerned, the risk is not so much from general surface corrosion but from deep pits. The pitting is likely when the feed water contains dissolved oxygen - the actual metal surface in a boiler that operates at over about 140 C has a magnetite oxide film that is highly protective and behaves in a similar way to the protective oxide films on aluminium and stainless steels, that is it is fairly impervious and also has similar thermal expansion properties to the base metal so it doesn't tend to spall off with thermal cycling. However, with excess oxygen in the feed water, very localised corrosion cells can be created that lead to deep pinholes being formed and eventual failure.
With 'proper' boilers, the feed water is always treated to remove dissolved oxygen. A device called a deaerator is used to scrub the dissolved oxygen from the water with low pressure steam and almost always a chemical oxygen scavenger is added, used to be hydrazine but less toxic chemicals are more common now. An important part of the commissioning procedure for high pressure boilers is the magnetite formation boil-out. Basically the boiler is fired with treated water, usually to give about 150 psi and the pressure maintained for 24 hours to get a good film of magnetite on the metal surface.
Unless you intend to operate the boiler over 500 C, then low carbon steel, A106 or similar, will be just fine. If you do want to go higher - unlikely but who knows, the grade known as P22. 0.5% Chromium, 2.25% Molybdenum is good to 560 C - from memory.
I'm not sure how relevant any of this is to model boilers as the corrosion processes are very slow and I think it rather unlikely that any model boiler would be operated for the 1000's of hours that would be needed to cause serious corrosion. Probably a much greater risk would be from general rusting when the boiler was sitting idle but that can be dealt with very easily. Either store it very dry or keep it full with water with a couple of percent of washing soda dissolved, provided you keep the pH above about 10 you won't get any rusting.
Regards, Hugh
Thread: Tapmatic Help
31/10/2011 09:28:47


Hi
Many thanks Andrew and Hansrudolf, I am very encouraged and looking forward to trying out my new toy. I have ordered an M12 x 1 spiral flute tap and, after a little revision of basic geometry, an 11.3 mm pilot drill - I was pleased when I checked my calculations for percentage of radial thread engagement with Machinery's Handbook and found that it agreed! The 11.3 mm will give me about 65% which is more than enough, even if the drill is a bit oversize.
Andrew, from your photo, I assume that the Tapmatic unit will try and rotate in the same direction as the quill(clockwise from above), hence the position of the stop bar to prevent this. Does the unit spin around when you reverse direction to remove the tap? Or put it another way, do I need to take cover when I move the quill up smartly to start it coming out?
Hansrudolf, I will definitely prepare a good supply of scrap pieces and practice until I have a feel for tapping this way.
I will have a go later this week when my tap and drill arrive and report back!
Thank you again gentlemen.
Regards, Hugh
28/10/2011 20:35:01


Hi Mick and Andrew,
Many thanks for the info. As far as teaching me to suck eggs, you won't go far wrong if you work on the assumption that I have never see an egg before, may have read about them in books but wouldn't recognise one if it jumped up and bit me - do eggs bite?
So, yes please to any other info on tapmatic and the like. If possible, a dummy's guide to tapmatic tapping would be incredibly helpful. Like how do you set the torque limit, do you use the self feed on the mill or just use the quill feed handle, etc, etc?
I will bite the proverbial and buy a spiral flute tap, presumably in EN1A I don't need any high performance coatings, just good old HSS?
Sorry to be a nuisance but as I have absolutely no background in machining, a lot - an awful lot - of what most would consider the Janet and John level of engineering skills just aren't there so the more basic the better.
Ta everso, Hugh
28/10/2011 18:26:28


Hi, I've just scored a Tapmatic 70X tapping head for my mill from fleabay. I have downloaded the instructions from the Tapmatic web site but they are a bit skimpy.
Does anyone have any experience with using these units? I have a fair number of M12 x 1 holes to tap in EN1A. Some through holes and some blind. Will I need to use spiral taps or will standard second or plug taps be OK?
All help gratefully received.
Regards, Hugh
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